An electromagnetic hand writing input device (or a hand writing system tablet) is typically used by a user with a tablet and an electromagnetic pen-type stylus (after, saying electromagnetic pen). The conventional electromagnetic pens are classified into the electromagnetic pen with a battery and the electromagnetic pen without a battery according to the methods of providing power. In the electromagnetic pen with a battery, a battery is provided to be the power source of this electromagnetic pen. The oscillator circuit in this electromagnetic pen with a battery actively emits the electromagnetic signals by the power provided by the battery. It is so-called active type electromagnetic pen. The electromagnetic pen with a battery has following advantages: (1) No matter the electromagnetic pen is near the tablet or away from the tablet, the electromagnetic pen can emit the electromagnetic signal with special frequency continuously. (2) No matter the electromagnetic pen is near the tablet or away from the tablet, the intensity of the electromagnetic signal emitted from the electromagnetic pen is maintained. (3) The intensity of the electromagnetic signal emitted from the electromagnetic pen is stronger as a result of the enough power provided by the battery.
However, the electromagnetic pen has a drawback of heavy weight. As a result that the electromagnetic pen has a need of a battery put in the body of the electromagnetic pen, for example a AAA size alkaline battery, the weight of the electromagnetic pen is increased because of the battery. Therefore, it is inconvenient for the user to operate and carry.
In the electromagnetic pen without a battery, there is no any battery existing in the electromagnetic pen for providing power to the electromagnetic pen. Instead, a LC resonance circuit is provided in the electromagnetic pen for receiving energy from the tablet. The LC resonance circuit resonates with the AC electromagnetic signal emitted from the tablet, and it receives electromagnetic energy and store energy in the oscillator circuit. After tablet stop sending energy, the electromagnetic pen begins to emit electromagnetic signal to the tablet by using the same LC resonance circuit with energy it stored. Therefore, this electromagnetic pen receives the electromagnetic signal and emits the electromagnetic signal by the same resonance circuit in this electromagnetic pen. However, the electromagnetic pen without a battery has only advantage of low weight, but it has many disadvantages as following: (1) The electromagnetic pen cannot receive enough electromagnetic energy and cannot emit the electromagnetic signal when the electromagnetic pen moves away from the tablet. (2) The intensity of the electromagnetic signal cannot be maintained, because the longer distance between the electromagnetic pen and the tablet, the less electromagnetic energy the electromagnetic pen can receive. Therefore, if electromagnetic energy received by the electromagnetic pen is not enough, the intensity of the electromagnetic signal, which is emitted from the electromagnetic pen to the tablet, is getting weaker. This electromagnetic pen only can emit the electromagnetic signal at a short time period because the electromagnetic pen only can store little energy. And during the period for emitting the electromagnetic signal, the intensity of the electromagnetic signal is getting weaker quickly because the power stored in the electromagnetic pen is reduced quickly. Therefore, the electromagnetic pen cannot emit the electromagnetic signal continuously and the intensity of the electromagnetic signal cannot be maintained in the period. (3) As a result that the electromagnetic pen only can store little power, the electromagnetic signal emitted by the electromagnetic pen is weak and it is easy to be interfered by the noises in the environment.
In recent years, there are some long-lasting batteries, for example a lithium battery, some rechargeable batteries which can be used repeatedly, and super capacitors have been developed instead of the dry battery in the electromagnetic pen with a battery. However, it has a need of rechargeable function in these designs of these electromagnetic pens, and it has a need of adding some extra components to the electromagnetic pens, for example a power managing unit, a recharging contact, and a recharging circuit, or some components which people can get easily, for example a super capacitor, in these electromagnetic pens. Therefore, the structures of these electromagnetic are complicated and the difficulty and cost for fabricating these electromagnetic are increased instead. However, even these designs are adopted, the weights of these electromagnetic pens cannot reduced substantially.
Therefore, in view of foregoing drawbacks of the conventional electromagnetic pens, there is a need to provide a new electromagnetic pen having characteristics of simple structure, low cost and low weight, and having advantages of both of the electromagnetic pen with a battery and the electromagnetic pen without a battery. It has no need to use a battery as a power source of the electromagnetic pen and it does not have the drawbacks of the electromagnetic pen without a battery.